1. Field of the Invention
The present invention is directed to a device for preventing a foreign object from being sheared or pinched when two parts which can move past one another approach one another, in particular, in the operation of loading and unloading stations in a clean room area or in its vicinity, in which a signal of a sensor interrupts the approach when the presence of a foreign object is detected in the region of approach.
2. Description of the Related Art
Safety devices for preventing injuries and damage during the operation of systems in which two parts move past one another at a slight distance are known primarily from the domain of heavy machinery construction and agricultural machinery construction and, as automation increases, are required in all industrial areas for the protection of men and machines.
In one method the danger zone is blocked off generally by screens and enclosures. When manual intervention cannot be avoided in one-man operation, a two-hand control may be a good solution. If it is compulsory that several persons be stationed in the danger area or if multiple machines are being operated, controls are used which either deflect intervention or terminate the movement of the machinery. Sensors such as light barriers, pressure hoses, contact tapes, motion alarms, feelers or the like, whose signals are used to switch off or brake the movement of the machinery, are used to detect the approach of a body.
DE 34 20 225 A1 uses a so-called end strip as a mechanical sensor in combination with switches for detecting foreign objects in the danger zone of a lifting platform. An arrangement at the moving part, the construction of switches as closers or contact makers and the lack of sensitivity of large end strips to the horizontal action of foreign bodies can be disadvantageous because a lateral deflection does not compulsorily result in a connection.
DE 36 06 499 C1, DE 38 43 478 C1 and DE 40 38 224 C1 make use of a pretensioned special safety strip as means for protecting against terminating edges. This safety strip has a plurality of contact elements arranged in a row, the electrical circuit formed by these contact elements being interrupted by the influence of external force. Difficulties arise when angles and small radii are present. Problems with the safety run-off occur at the ends of the safety strip.
DE 37 25 360 A1, DE 28 54 459 and DE 41 21 916 A1 are disadvantageous in that the closer functions as a contact or as a result of the high cost for monitoring operation.
In order to afford protection from shearing edges of platform parts moving vertically relative to one another, DE 39 28 984 C2 makes use of a taut track which extends downward and has a control element which detects movement of the track. This invention is too bulky and imprecise for special use, e.g., in local clean rooms under the conditions required by so-called SMIF systems (Standard Mechanical Interface described, e.g., in DE 43 26 309 C1). Further, an air flow which is required in these SMIF systems can adversely affect the reliability of such a solution. In such systems, it is necessary in particular to avoid penetration of foreign objects in the region located between an upper frame and the descending or ascending base acting as platform.